This invention relates to compensation for patient or other movement in computed tomography equipment and operation, and in particular to an improved method for mitigating blurring and streaking in computed tomography (hereinafter "CT") caused by movement of the object being imaged or the CT equipment during imaging.
Blurring and streaking caused by movement during imaging is a well-known, but difficult to solve problem in CT equipment. Such movements, in the case of medical CT imaging may be, for example, patient movement. The principle present solution to the problem is attempting to avoid movement during imaging. This includes in the case of medical CT imaging breathholding by the patient to briefly avoid the patient's periodic motions, such as respiratory activities. However, such techniques are generally not particularly useful and applicable to critically ill patients, infants, and involuntary organ motions. Various attempts to minimize the problem include efforts to design faster scanning equipment not as susceptible to movement problems, but which is necessarily more complex and expensive and which does not enhance resolution; the use of volummetric CT based on cone-beam and planar detector arrays; attempts to measure the motion to compensate for it; and post-processing the image data obtained with algorithmic approaches. These techniques have not proven able to handle all possible patient motions such that the various approaches to solving the problem of patient motions have not proven entirely satisfactory. In addition, there are other odd categories of motion perturbations such as the equipment platform or mechanical jittering when, for example, a heavy truck passes the building or room in which the equipment is positioned, cardiac and respiratory motions, and a shift of X-ray focal spot. It becomes extremely diffcult to provide sensors which can measure such movements as a basis for compensation of the movements. As a result, it is desirable that a compensation method not be based on the addition of motion sensors or detectors and the measurements or signals provided by motion sensors or detectors.
In addition, it is highly desirable that any compensation provided for patient movement be applicable not only to the design and construction of new equipment, but also to be applicable and suitable for readily retrofitting or incorporating into existing CT equipment because of the considerable number of existing CT equipments which exhibits blurring, streaking, and poor image resolution as a result of patient motion (i.e, expansion and contraction). Moreover, it is highly desirable that motion compensation equipment and methods be applicable to both parallel and fan beam scanning systems, and also to cone scanners.
It is also desirable that the method for compensating for movement in CT equipment be relatively uncomplex and relatively inexpensive to facilitate its ready incorporation into various types of CT equipment, including existing equipment. Although there are a wide variety of motion functions, the type of problem dealt with by this invention is limited to (1) motions occuring in the same plane defined by the position of the X-ray beam in two dimension CT and (2) motion occuring within the same cone defined by the X-ray source and the detector array. Correction for translational motion only is discussed in W. T. Lin "A Motion Compensation Algorithm for Arbitrary translation of CT Objects", SPIE Medical Imaging, 1994, Feb. 13-14, 1994, Newport Beach, Calif., pp. 743-754.